Objectives: To summarise and critically evaluate the evidence from randomised clinical trials (RCTs) of t'ai chi as a treatment for patients with osteoarthritis (OA). Design: Eleven databases were searched from their inception to July 2010. RCTs testing t'ai chi against any type of controls in human patients with OA localised in any joints that assessed any type of clinical outcome measures were considered. Two reviewers independently performed the selection of the studies, data abstraction and validations. The risk of bias was assessed using Cochrane criteria. Results: Nine RCTs met the inclusion criteria, and most of them had significant methodological weaknesses. Six RCTs tested the effects of t'ai chi compared with that of an attention-control programme, a waiting list and routine care or self-help programmes in patients with OA in the knee. The meta-analysis suggested that t'ai chi has favourable effects on pain (n=256; standard mean difference (SMD), −0.79; 95% CI −1.19 to −0.39; p=0.0001; I2=55%), physical function (n=256; SMD, −0.86; 95% CI −1.20 to −0.52; p<0.00001; I2=38%) and joint stiffness (n=256; SMD, −0.53; 95% CI −0.99 to −0.08; p=0.02; I2=67%). Conclusion: The results are encouraging and suggest that t'ai chi may be effective in controlling pain and improving physical function in patients with OA in the knee. However, owing to the small number of RCTs with a low risk of bias, the evidence that t'ai chi is effective in patients with OA is limited.